Energy Efficient Operation Strategies to Optimize Cooling Tower Performance

Cooling towers work as lungs in an air conditioning chiller plant. Ambient air comes in contact with condenser water at cooling tower fills. Impurities in air collect at the bottom and circulate in the system. These may deposit on chiller condenser tubes or inside pipe lines when unattended. Constant vigilance and precautionary measures are required to improve plant performance and increase cooling tower and plant life. Overall energy consumption by the chiller depends on cooling tower performance. When cooling tower performs well and provides condenser water to chiller as required, chiller energy consumption is low. A badly performing tower increases condenser water temperature to the chiller, which increases the chiller energy consumption for same output.

Cooling Tower hot water basin has multiple inlets. Water from chiller is distributed on top of fills. When water distribution is not balanced in each inlet pipe, cooling tower can not deliver 100% performance. Balancing valves are provided in each line. Water coming from main line is equally distributed in each branch. Fills on all sides are fully loaded. Without this balancing, one side will get more water than the other and water temperature can not be brought down as required.

Debris and scale deposit on hot water distribution nozzles. All nozzles are required to be clean and providing equal flow. Damaged or clogged nozzles give uneven flow, which keeps some areas of the fills dry. Sunlight propagates growth of algae in hot water basin. This algae circulates everywhere in the system. Hot water basin is covered during operation or in idle conditions. Direct daylight is avoided. This reduces algae growth. Air intake side of the towers is one of the reasons for badly performing towers. Most of the time, architects consider cooling towers as ugly and noisy equipment in a building. They provide space at a location where there are solid walls around. Solid walls restrict air flow. When towers are places close to a wall, this is louvered. Free flows of air around towers provide rated duty. Manufacturers provide data about safe distance of the towers from solid or louvered wall.

For water saving, cycle of concentration (COC) is increased. With increased cycle of concentration, say from 3 to 4, blow down rate is low and chemical usage is high. A very delicate balance exists when deciding about COC. Make up water chemistry, water availability and costs of chemicals are all considered for deciding about optimum COC. For more water conservation it may be increased further.

Correct blade angle and material of the fan save operating energy when properly selected. FRP blades are most efficient. Blade angle is optimized for each season. VFD operation of the fans with proper control sequence provide maximum energy saving.